Fed by four alpine glaciers, Fox Glacier falls 2,600 m (8,500 ft) on its 13 km journey from the Southern Alps down to the coast, with it having the distinction of being one of the few glaciers to end among lush rainforest only 300 metres (980 ft) above sea level. Although retreating throughout most of the last 100 years, it has been advancing between 1985 and 2009. In 2006 the average rate of advance was about a metre a week. In January 2009, the terminal face of the glacier was still advancing and had vertical or overhanging faces which were continually collapsing.Since then there has been a significant retreat, with the 2009 high level clearly visible as vegetation line on the southern slope above what is left of the lower glacier today.
The outflow of the glacier forms the Fox River. During the last ice age, its ice reached beyond the present coastline, and the glacier left behind many moraines during its retreat. Lake Matheson formed as a kettle lake within one of these.
The Southern Alps is a mountain range extending along much of the length of New Zealand’s South Island, reaching its greatest elevations near the island’s western side. The term “Southern Alps” generally refers to the entire range, although separate names are given to many of the smaller ranges that form part of it.
The range includes the South Island’s Main Divide, which separates the water catchments of the more heavily populated eastern side of the island from those on the west coast. Politically, the Main Divide forms the boundary between the Canterbury and West Coast Regions.